2006 Annual Report 4d.Progress report. Laboratory and plant growing facilities progressed with the installation of six 1000-litre glass pools and a new successful planting technique. Several natural enemies are under consideration as biocontrol agents: 1- Hydrotimetes natans. This weevil feeds on the plant tips while the larvae mine the plant stems. At high densities it causes a lot of tip damage. Larvae and most adults were found only in C. caroliniana; a few (< 3%) can also be found on E. najas and Utricularia platensis Spegazzini (Bladderwort), which frequently grow intertwined with C. caroliniana. Adults have been released in tanks with Egeria densa and Eichhornia azurea for non choice tests. No larvae or pupae were ever observed, nor were the adults released recovered in inspections when the tanks were cleaned. This and field evidence of other aquatic plants co-occurring with C. caroliniana, reinforce the idea that this weevil is quite specific to fanwort. 2- Paraponyx sp. The gilled larva of this moth feeds on the terminal shoots of Cabomba, causing a characteristic damage that stunts each individual stem’s growth. The larva is very hard to detect because of its cryptic habits. This species has not been found on other plants collected together with Cabomba. However, it was identified as Paraponyx diminutalis (Snellen), which is native to Sri Lanka, and is considered a pest of Nymphoides cristatum in India. It is found on Hydrilla verticillata in the U.S., and has been found to feed on Cabomba in host range experiments, though apparently not in the field. 3- New Pyralid. A new species of moth has been recently discovered forming small case with leaf fragments, and feeds in the shoots. It remains unidentified. Final considerations on some natural enemies: We discarded one of our main candidates, the moth Paracles nr. burmeisteri. Experiments showed it can feed on Egeria densa and on many other aquatic plants with foliage in the water (Cabombaceae, Hydrocharitaceae, and Pontederiaceae). The following insects were frequently collected, identified and their habits sought in the literature or observed in the laboratory: 1- Rhopalosiphum nymphaeae L. (Hemiptera: Aphididae): This aphid (water lily aphid) is a common pest of at least 20 species of aquatic plants. 2- Hedriodiscus chloraspis Wiedemann (Diptera: Stratiomyidae): The larva of this soldier fly is a filter feeder, feeding mostly on algae. The scratching of the mouth pieces can cause some damage on fresh plants, especially at high densities, but it is by no means a suitable biocontrol candidate, due to its negligible damage and complete lack of specificity. 3- Ephydra riparia Fallen (Diptera: Ephydridae): A similar description to H. chloraspis applies to this common insect. Field Ecology: A definite succession was observed within the submerged plant community in Cabomba environments. We observed that the coverage of Egeria najas increases during the summer from almost 0% in early spring, to 20 - 40% by Fall. This responds to water turbidity increases with the water temperature during the Summer, thus benefiting the shade tolerant Egeria plants. Likewise, the Cabomba stands found in more open and clear waters rarely have E. najas mixed with them, even during the summer. In several small lakes and ponds, we observed a steady replacement of Cabomba by E. najas. Ponds that had approximately 50% of each species now show a complete dominance of E. najas, with Cabomba coverage reduced to less than 0.01%.